Apple released 3.1 with not so many feature enhancements. Please refrain from updating either iTunes or iPhone firmware using automatic updates. These will soon be patched for continued jailbreak and unlock support.
If you update, you may permanently lose any chance of unlock (atleast for months!). The following screenshot by Musclenerd of Dev Team fame proves that baseband for iPhone 3.1 can already be preserved. So, sit tight and wait for an updated firmware or better yet, pwnage tool to tailor an ipsw yourselves!